IAD02FA091
NTSB Identification: IAD02FA091.
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Accident occurred Sunday, September 08, 2002 in Byram Township, NJ
Probable Cause Approval Date: 10/27/2005
Aircraft: Piper PA 32R-301T, registration: C-GKLY
Injuries: 2 Fatal, 2 Serious.

The airplane was in cruise flight at 3,500 feet mean sea level when the engine lost power. The pilot then performed a forced landing to trees. Examination of the Lycoming IO-540 series engine revealed that the zinc-plated crankshaft gear attachment bolt was fractured, and that the crankshaft no longer drove the gear. Fracture surface analysis revealed intergranular separation due to hydrogen-assisted cracking. Engines had previously been built with cadmium-plated bolts, but zinc-plated bolts were being used because they were readily available, and had a "positive impact" on production. Lycoming received 8,500 zinc-plated bolts between November 1996 and July 1998. Lycoming manufactured or re-built/overhauled 1,088 engines with zinc-plated bolts, and shipped 2,667 zinc-plated bolts as spares. Two zinc-plated gear bolt failures were documented in helicopter engines in 1998, due to hydrogen embrittlement. One bolt failed at 30 hours of operation, and the other at 19 hours. Lycoming and FAA personnel believed the failures occurred due to the higher loads generated by helicopters. Based upon the two failures, Lycoming removed the bolts from its stock as a "precautionary measure" in July 1998. Bolt recalls were issued by the helicopter manufacturer and Lycoming in July 1998. The FAA issued an Airworthiness Directive (AD) in February 1999 to replace the crankshaft bolts in affected helicopter engines worldwide. In July 1999, a Piper PA-32R-301 bolt failed due to hydrogen embrittlement at 327 hours. Between March 2000 and January 2001, two bolts failed on Royal Jordanian Falcon trainer airplanes, at 292 and 179 hours. As a "precautionary measure," Lycoming replaced the crankshaft gear bolts in the five-airplane Jordanian Falcon fleet about February 2001. Lycoming and FAA personnel believed the failures did not extend beyond helicopter and aerobatic applications, although the PA-32R-301 failure occurred in 1999. In June 2002, another bolt failed on a Piper PA-32R-301, at 448 hours. The engine was examined by Lycoming and FAA personnel, and a Lycoming laboratory report stated the failure was due to hydrogen embrittlement. In September 2002, this accident occurred, and as a result of the investigation, about 2 weeks after the accident, Lycoming issued a Service Bulletin (SB) to replace bolts on certain 540-series engines. In October 2002, the FAA issued an Emergency AD to also replace the bolts. The common cause for hydrogen embrittlement is a missed or under baked condition.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:

the improper manufacturing of the crankshaft gear bolt, which resulted in the failure of the bolt due to hydrogen embrittlement, and the subsequent loss of engine power. Also causal was the engine manufacturer's failure to remove the affected bolts from fixed wing engines during the 4-year period that transpired between the initial failures and removal of the bolts from stock for installation, until the accident flight. A factor in the accident was inadequate oversight (lack of action) by the FAA during the 4-year period in which the bolts remained in serviceable engines.

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